The present invention relates to a method for the manufacture of foil capacitors made by the stacking of metallized plastic films as well as to the capacitor obtained by such a method.
As shown in FIG. 3, one of the steps of the method consists in the coiling or winding, on a large-diameter wheel S, of at least one pair of metallized plastic films F1 and F2. Each metallized plastic film takes the form of a strip cut from a large width of metallized plastic film. During this winding stage, a non-metallized side margin M1, M2 is made on each of the two films of the pair (FIG. 4). The non-metallized side margins are made on opposite sides in order to obtain a pair of films constituted by an even-order film and an odd-order film.
Thus, a capacitive strip comprising alternating even-order and odd-order layers, called a parent capacitor is obtained and is shown in front and side elevations in FIGS. 5 and 6. Each of the lateral faces L of the capacitive strip is then covered with a metal or an alloy in order to make output plates. Each output plate enables the metallizations of the same-order layers to be connected to one another mechanically and electrically. This operation, which is achieved by the spraying of molten metal, is known as Schooping or Schoop's metal process. To obtain more efficient clinging of the drops of molten metal to the same-order films, it is recommended that the even-order films should be offset with respect to the odd-order films as shown at d.
As shown in FIG. 7, the parent capacitor is then cut out along lines D1 and D2 into elementary blocks shown in FIG. 8. Each capacitor constitutes a foil capacitor with a generally parallelepiped shape comprising two metallized lateral faces that constitute the plates as shown in FIG. 8.
Then comes the step of soldering the connections to each of the plates of the capacitor.
According to the prior art, the technique of soldering to plastic film capacitors uses the process of reflow, by electric arc or laser beam, of a tin-lead alloy deposited by Schooping on the film capacitor. In melting through the energy provided, the tin-lead alloy ensures quality of the electrical contact and the mechanical behavior (i.e. characteristics of strength and resistance) of the connections on the capacitor.
The capacitor is then encapsulated in a pack by means of a thermosetting resin or is covered with epoxy resin by the so-called fluidized bath method.
The soldering technique described here above has several drawbacks:
it requires the bringing together of two electrodes of the parts to be connected, thus restricting the work rate; PA1 it calls for frequent operations to clean said electrodes so that a minimum quality of solder joint is maintained. PA1 coiling at least one pair of metallized plastic films so as to form the stacked structure of the capacitors; PA1 metallizing the lateral faces of the coiled structure in order to create the plates of the capacitors; PA1 cutting out the coiled and metallized structure, or parent capacitor, into semi-finished capacitors; PA1 putting the semi-finished capacitors and their connection wires through a cleansing flux; PA1 soldering the connection wires to the plates of the semi-finished capacitors;
According to the prior art soldering method, it is difficult to obtain high-quality mechanical behavior for the connections. The low-quality mechanical behavior of the connections then results in poor electrical contact which causes deterioration in the loss angle of the capacitors.
These drawbacks arise chiefly out of the fact that the reflow of the alloy deposited on the two sides of the plastic film capacitor is only localized and corresponds to the dimension of the electrode or of the laser beam.
The invention does not have these drawbacks.